Nonmetallic armor



April 1949. s. L. KROPSCOTT ETAL 2,466,597

NONHE'I'ALLIC ABIOR Filed Nov. 27, 1944 INVENTORS Arno/JR. Gab e/ yfar/e L. Kro O$co// W w$d A TTORNE Y5 Patented Apr. 5, 1949 NONMETALLICARMOR Earle L. Kropscott and Arnold R. Gabel, Midland, Mich., assignorsto The Dow Chemical Company, Midland, Mich., a corporation of Delaware 'Application November 27, 1944, Serial No. 565,428

Claims. 1

This invention relates to a composite article of high impact strength,and more particularly to a non-metallic structure suitable for use as alightweight armor for protection against low velocity projectilles.

Becaus of the high density of metal armor plate, the effectiveprotection afforded by a unit weight is very low. A large effective areaof protection per unit weight of armor is important especially inpersonal or body armor and in armor for air raft. Personal armor must belight, to be carried easily, and in military uses it must not interferewith a soldiers ability to carry his normal accoutrements. Aircraftarmor must afshould have continuous adherence between the successivelaminae, whereas, for the purpose of the present invention it isdesirable that the adherence should be to a certain extent discontinuousso as to yield progressively from layer to layer untfl the force of theimpact is absorbed, and fracture of the structure on impact of theprojectile must be avoided. Laminates having continuous adherencebetween the layers are more easily penetrated by bullets than those ofthe present invention, which are less rigidly bonded. The quality ofdiscontinuous lamination possessed by th articles of the presentinvention produces an internally yieldable struci'ord protection with aminimum resultant deture which is herein defined as an internally creasein effective speed, range, or carrying yieldable lamination. capacity.The fibrous glass textile for use in the in- The major purpose of bothpersonal armor and vention, it has been found, must be of the conaimraftarmor is to deflect or stop such low tinuous filament type, sinctextiles made from Velc. ty projectiles as spent bullets, shrapnel,instaple glass fiber, chopped fiber, or staple scrap cluding the typeknown as flak," and bomb do not afford adequate .protection whenincorsplinters, all of which account for a greater proporated inlaminated structures of the type here portion of the injuries to combatpersonnel than concerned. It has been found, as well, that the do directhits by aimed projectiles. The velocidegree of protection, in otherwiseequivalent ties of such low velocity projectiles are usually structures,increases as the diameter of the conless than 1200 feet per second.tinuous glass filaments decreases. Thus, using It is accordingly amongthe objects of the presone commercial designation, a "450 yarn is entinvention to provide a relativelyv lightweight superior to a "250 yarn"in woven glass textiles and nonmetallic armor suitable for protectionfor the present purpose, the former being made against low velocityprojectiles. The provision of filaments roughly half the diameter ofthose of suitable compositions of matter and of a in the latter yarn. Ithas also been found that, method of producing the desired articles isconwhile good results can be and are obtained when sidered tobe arelated object. Other objects may using textiles in which both the warpand the become apparent from the following description weft are of glassfiber, improved results are and the apended claims. obtained when usingtextiles having a warp of It has now been found, in accordance with thecontinuous glass filaments twisted into multi-filapresent invention.that a suitable lightweight and ment yarns and a weft or filling ofcotton. Satisnonmetallic armor may be made, which gives effactory typesof glass textiles are those which fective protection against lowvelocity projecare known commercially at "0C" and "ECG" tiles, and whichmay be formed to any desired types. particularly "QC-64," QC-111, andshape and size by simple compression molding "ECC-l1-127," as made andsold by the Owensoperations. The armor of the present invention CorningFiberglas Company. comprises a composite multilayer structure of a Theethyl cellulose composition used in bindcertain typ of fibrous glasstextile and a paring together a number of sheets of the preferredticular class of ethyl cellulose composition, to be glass textile shouldbe one which is adapted for described more fully hereinafter. It may beprocompre sion m n Op r ions. and should convided in thicknessesadequate to stop many sotain agents cap ble of preventing the h mateen dhigh velocity projectiles, rial from sticking to the mold, in quantitiessum- The composite, multi-layer structure may, for cient to preventperfect or continuous laminaconvenience, b described as a laminatedproduct, tion. for the reasons previously mentioned. More but it shouldbe made clear that, as compared sp cifi lly. it has n found t e powithmost laminates common in the art, this sition should contain from topercent of an product would not be considered representative of ethylcellulose having an ethoxy value of from a ver high quality oflamination. This is true 47 to 49 per cent. and should b of a type whosebecause, for most purposes a laminated article 55 5 per cent solution,by weight, in a mixture of 3 80 parts of toluene and parts of ethanol,by volume, has a viscosity between 50 and 150 centipoises, and moreadvantageously between 80 and 120 centipoises. Ethyl cellulose in thelatter viscosity range will be referred to herein as "100 centipoisetype." The composition should contain from 1 to 6 per cent of a moldrelease agent, and, when applied as a lacquer to the glass textile, thedope should contain, on the solids basis, from 4 to 6 per cent of suchagent. The mold release agent may be stearic acid alone, when amounts ofabout 1 per cent are used, but is more advantageously a mixture of equalparts of stearic acid, magnes um stearate, and the methyl ester ofl2-hydroxy stearic acid. The total of ethyl cellulose and mold releaseagent should be at least 85 per cent. The balance of the solids in thecomposition, which may vary from 4 to 15 per cent, is a solvent type ofplasticizer for the ethyl cellulose, which may, but need not, be aphthalate or a phosphate plasticizer, and which, in the most effectivecompositions yet found for the purpose, is mono-phenyl diorthoxenylphosphate. In addition to the above requirements as to composition, aphysical requirement is that the composition, when subiected to 1500pounds pressure per square inch, at a temperature of 110' 0., must fiow1.5 inches in from 70 to 160 seconds, as measured in ASTM D-569-43.

The laminated structure may be prepared by a molding operation. Ifdesired, alternate layers of a previously prepared film'of an ethylcellulose composition and of the fibrous glass textile may be placed ina suitable mold and compressed under the conditions of temperature andpressure which will be described later. Generally speaking, however, itis more advantageous to dissolve the ethyl cellulose composition in asuitable lacquer solvent to prepare a coating dope and to apply a thincoating of the composition to the glass textile. This may be done byspraying, brushing, or any of the standard machine coating operationsand. for the particular method employed, the composition will bedissolved to form the most appropriate viscosity solution. In coatingthe glass textile, it has been found that the ratio of coatingcomposition to glass should be so chosen as to provide a dried articlewherein from '10 to 80 per cent of the weight is theglass textile andcorrespondingly from to 20 per cent is the ethyl cellulose composition.Lesser amounts of the ethyl cellulose composition apparently do notprovide adequate adhesion between thelayers of glass textile in thefinished product, while greater quantities eflect too great a cementingaction on the successive layers of-fibrous glass and prevent thenecessary yielding of the composite article when struck by a projectile.The most satisfactory articles which have been prepared from thestandpoint of their use as armor have been found on analysis to consistof from 65 to 80 per cent of material which is neither decomposed norvolatilized when heated in a furnace at 1000' F.

In commercial operation, the fibrous glass textile is coated either inthe form of individual sheets or as a continuous roll with the ethylcellulose composition and dried at a moderate temperature to remove thevolatile solvents. The sheets are then cut to the desired shape and sizeand are superimposed one on another until enough material is so stackedto provide the required final thickness after molding. It is preferable,in this glass textile at right angles to the adjacent layers. Articlesof equivalent strength but of higher density may be made by plying twosheets in one direction and then two at ri .t angles to the first pair.The assembly is placed in the cavity of a compression mold and preheatedin the closed mold without application of any appreciable pressure untilthe temperature of the entire assembly has been brought to at least 360F. This may require a period of from 3 to 12 minutes or longer.depending upon the thickness or the article. When the final molding isto be 1; of an inch thick, 9. preheating period of from 8 to 10 minutesis usually satisfactory. After preheating, as above described, pressureis applied to compress the sheets and to cause cohesion therebetween.Satisfactory pressures are in the range from 500 to 2000 pounds persquare inch and the most consistent results are obtained with pressuresfrom 1500 to 2000 pounds. No appreciable advantage is obtained throughthe use of higher pressures and a distinct disadvantage results from theapplication of more than a few hundred pounds pressure during thepreheating operation. It is only necessary to maintain the moldingtemperature of from 350 to 380 F., and preferably from 360 to 370' F.,for from 1 to 3 minutes after the high pressure is applied. Thatpressure is then maintained while the molded article is cooled at leastto a temperature below the distortion point of the plastic composition.The so-prepared article may then be ejected from the mold and is readyfor use, possibly after further fabrication operations, as an armor forprotection against low velocity projectiles. Large sheets of thematerial so molded may be used as floor plate in aircraft while smallersizes cut to suitable shapes, may be used to surround the pilot'scompartment in aircraft or may be employed with suitable padding aspersonal armor, in vests, helmets or like articles.

One preferred embodiment of the invention is illustrated in the annexeddrawing, wherein Fig. 1 is an isometric view in exaggerated scale of thenew laminated article, with three layers peeled back to illustrate thestructure; and

Fig. 2 is a greatly exaggerated section tthrough two layers of the newarticle.

In the said drawing, a glass fabric 3, having continuous multi-filamentglass warp l and cotton filler 8, is coated with the herein describedethyl cellulose composition 6, and bonded to a similarly coated fabricturned so that the warps 4 in successive layers are at right angles toone another. The composite article I may be used as lightweightnonmetallic armor. The quality of discontinuity in the laminate isillustrated in Fig. 2 of the drawing by the double line about thecontinuous glass warps 4. representing imperfect lamination due to theamount of mold release agent originally in the composition 8.

Numerous tests have been made to determine the protective power of thelaminated structures of the present invention. While these laminatedstructures have beenmade in thicknesses ranging from about 1*; of aninch up to 1% inches, preliminary tests for purposes of comparison withother armoring material such as aluminum or steel have been made onsmall samples approximately 6 inches square by 0.1. or 0.2 inch thick.It has been found that, when a laminated article 0.1 inch thick has beenmade in accordance with the present invention, it will stop a .45caliber revolver bullet fired at pointblank range of 10 feet. Withoperation. to align successive layers of the coated -76 the powder loadused in the standard tests, this was indicative of an ability to stopprojectiles having a velocity of from 850 to 1000 feet per second. Asample which would pass this test was considered satisfactory forfurther testing at velocities exceeding those normally encountered withrandom projectiles.

The following examples illustrate the manner in which the articles oithe present invention may be made and describe some of the tests towhich such articles have been subjected.

Example 1.A continuous sheet of a fibrous lass textile 36 inches widehaving a continuous filament warp and a cotton filler (Owens-CommaFiberglas Company OC-64) was coated to provide a finished sheet of which80 per cent by weight was the glass textile and 20 per centwas an ethylcellulose composition containing the following parts by weight: ethylcellulose (48.3 per cent ethox 100 centipoises) 82 per cent, plasticizer(mono-phenyl di-orthoxenyl phosphate) 12 per cent, stearic acid 2 percent. magnesium stearate 2 per cent, methyl 12- hydroxy stearate 2 percent. The coating was deposited from a solution in a solvent consistingof 80 parts of toluene and 20 parts of ethanol by volume. The sheet wascut into thirty sixinch squares when dry. Twenty-one such squares werestacked with the glass warp in each layer at 90 to that in adjacentlayers. The assembly was preheated to 360 F. for ten minutes and thenplaced between polished plates at 1500 pounds per square inch for twominutes while maintaining the temperature at 360 F. after which thepress was cooled under pressure until the temperature of the laminatewas below 120 F. when it was finally removed from the mold. Thisnonmetailic armor had a thickness of 0.188 inch and a density of 1.80.Samples cut from the sheet were hung in a ballistic pendulum to measurethe velocity of the projectile at impact and were fired upon using anon-deformable chilled steel ball 0.219 inch in diameter fired from a.22 Hornet" rifle using a hand-loaded powder charge. The test method wasbased on that described by C. Panseri, in Light Metals" (London), vol.4, page 234, December, 1941. Average values of 1505 feet per second wereobtained as the limit velocity of the projectile which the laminatecould withstand. By way of comparison, a sheet of aluminum alloy No.24-51 oi the same thickness (0.188 inch) when tested with the sameprojectile under like conditions has a limit velocity of 1900 feet persecond. On a weight basis, the laminate of this invention is 18 per centmore efficient than is the aluminum, as may be seen from the followingcalculation wherein the figure 2.7 is the density of aluminum and 1.8 isthe density of the nonmetailic laminate.

without sacrificing protection, and a correspond-' ingly heavier payload may be carried.

Example 2.Several sheets of the same fibrous glass textile as wasemployed in the preceding example were stacked one above another withthe warp in each layer at 90 to that in adjacent layers. Betweensuccessive layers of the fibrous glass textile were inserted sheets ofan ethyl cellulose film .000 inch thick containing 86 per cent of ethylcellulose having an ethoxy content of 48.5 per cent, 15 per cent of thesame p phate plasticizer as was employed in the preceding example, and 1per cent of stearic acid. This assembly was placed in a mold, preheatedfor 8 minutes at 370 F., and subjected to a pressure of 1500 pounds persquare inch at that temperature for 2 minutes, after which the laminatewas cooled and removed from the mold as before. The finished article inthis instance had a thickness of .122 inch and a specific gravity of1.61. Samples of the so-formed article were tested for their resistanceto the impact of projectiles in the manner described above and limitvelocities having average values of about 1000 feet per second wereobtained.

By way of comparison. the limit velocity of a similar thickness ofaluminum sheet, when tested with the same projectile, is about 1400 feetper second. A calculation similar to that set forth in the precedingexample indicates that the nonmetailic armor of this invention is 120per cent as eilective on a weight basis as is an aluminum sheet of thesame thickness.

Example 3.In a manner similar to that set forth in Example 1, laminateswereprepared in various thicknesses from 1* to /4 inch, and werecompared with aluminum sheets of the same thicknesses. The datarespecting limit velocities, and relative efliclency of the nonmetailicarmor. computed as in the preceding examples, are given in the followingtable.

Limit velocity/eel. per second N talll A] i onme e um num stopp ng zLaminate Sheet power,

d-LBO d-2.70 unit we ght (Al-100%) Per Cm! .0625 750 900 124. 5 .100 980i, 250 N7. 5 .128 1.150 1, .500 115. .160 L300 1,050 118.2 200 1,6502,000 124. .220 l,800 2,160 125. 5 .260 2,000 2,380 126.5

' tablish precise standards for tests under such conditions, sufficientevidence has been obtained to indicate a marked superiority of the newlaminated structures over aluminum plate of equal thickness when struckimilarly glancing 4 blows by similar projectiles of equal velocities.

By way of contrast with all of the foregoing data respecting the articleof the present invention, tests were made of the stopping. power ofarticles with other cellulose derivative binders, and of ethyl celluloseslabs alone. To illustrate, a laminate such as that here claimed butwith a binder of cellulose acetate of the AR-M type, having a thicknessof 0.173 inch, and tested as were the articles of this invention,withstood proiectiles only up to 1080 feet per second. A slab of ethylcellulose composition of the type used in this invention, but withoutthe glass textile,

had a limit velocity of only 760 feet per second at a thickness of 0.77inch. A similar slab of anothe type of ethyl cellulose composition,normally used for making moldings with high impact strength at lowtemperatures, had a limit velocity of only 460 feet per second.

The armor of the present invention need not be, and seldom is, employedin the form of a flat sheet. After lamination has been effected, it ispossible to impart curved shapes to such a structure by compressionmethods carried out in suitable forming apparatus at temperatures in therange from about 220 to 300 F. In this manner helmets, vests, andvarious shields may readily be produced.

The invention has been illustrated with respect to the use of fibrousglass textiles having continuous glass warp and a cotton or a glassfiller. There may be employed instead a specially prepared textilecomprising a continuous glass warp and an ethyl cellulose compositionfiller in the form either of thread or fiat tape. Such a textile can belaminated to other sheets of like material without the necessity for aspecial coating operation. It has been found that little if any strengthis contributed to the laminated articles by the cotton filler in theuni-directional textiles which have been employed. The substitution ofan ethyl cellulose thread for .the cotton thread results in the removalof a certain weight of material which is useless from the standpoint ofthe finished armor and permits the production of a more efficientlaminated structure.

In another modification of the invention, con.- tinuous glass filamentsmay be drawn and during their production deposited while still warm on amoving sheet of ethyl cellulose in which the filaments may be imbeddedby virtue of their temperature or by means of slight pressure. This mayprovide a sheet fully equivalent to the coated textile described in theexamples given above.

It has been observed that the fibrous glass textiles which arecommercially available are treated with a sizing agent to facilitatehandling and fabrication operations. In some cases that slzing agent isa high molecular weight aliphatic amine. Samples of fibrous glasstextiles have been obtained without sizing and, while it has been foundpossible to produce the armor of the present invention with an unsizedfabric, it is believed that better performance is obtained from a anarmor in which the glass fibers carry a sizing agent of the type whichis commercially present on glass textiles.

An advantage of the present invention which has not been mentionedheretofore is the nonsplintering characteristic of the present armorwhen it is punctured by a high velocity projectile. When punctured, fewparticles separate from the sheet and these are relatively nonindurious.This is in marked contrast with the properties of metallic armor plateswhich are known to produce sharp fragments when punctured. This is ofconsiderable importance, for example, in an airplane where the presenceof fragmentation particles will greatly increase the hazard of injury tothe personnel.

Preliminary medical reports indicate that.

when the present armor is punctured by a proiectile, no systemicreaction results from small particles of the laminate which may bedriven into and become imbedded in the flesh. This is in contrast to thewell-known complications which arise from particles of steel, brass, oraluminum under like circumstances.

We claim:

1. A nonmetallic armor for protection against low velocity projectiles.comprising an internally yieldable laminated structure of which from 70to per cent is a plurality of layers of a fibrous glass textile having acontinuous filament type of warp and having a cotton filler, andcorrespondingly from 30 to 20 per cent of a binding agent containingfrom 80 to per cent of ethyl cellulose having an ethoxy content of from47 to 49 per cent and a viscosity between 80 and 120 centipoises whenmeasured as a 5 per cent solution in 80:20 toluene-ethanol. from 4 to 6per cent of a mold release agent comprising stearic acid and magnesiumstearate, and the balance, not to exceed 15 per cent, of a solventplasticizer for the ethyl cellulose.

2. The article as claimed in claim 1 wherein each layer of the fibrousglass textile is turned with its warp at 90 to those of adjacent layers.

3. The article as claimed in claim 1 wherein pairs of layers of thefibrous glass textile are provided with their warps in alignment andeach such pair is turned with the warps therein at 90 to those ofadjacent pairs.

4. The article as claimed in claim 1 wherein the mold release agentconsists of approximately equal parts of stearic acid, magnesiumstearate and the methyl ester of 12-hydroxy stearic acid.

5. The article as claimed in claim 1 wherein the binding agent is amixture of about 82 per cent of ethyl cellulose having an ethoxy contentof about 48.5 per cent and a viscosity of about centiDOises whenmeasured as a 5 per cent solution in 80:20 toluene-ethanol, about 6 percent of a mold release agent consisting of approximately equal parts ofstearic acid, magnesium stearate and the methyl ester of 12- hydroxystearic acid and about 12 per cent of mono-phenyl di-orthoxenylphosphate.

EARLE L. KROPSCO'I'I. ARNOLD R. GABEL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,982,787 Cherry Dec. 4, 19342,372,983 Richardson Apr, 5, 1945 2,377,846 Dreyfus et a1. June 5, 19452,381,542 Hyatt et al. Aug. 7, 1945 FOREIGN PATENTS Number Country Date396,405 Great Britain Aug. 2, 1933 OTHER REFERENCES Article in ModernPlastics" of May, 1944, P es 100-108.

Ethocel Handbook published in 1940 by the Dow Chemical 00., Midland,Michigan, pages 28 and 32.

